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Orbital order due to Hund's rule frustration in Kondo lattices

Event Details

Event Dates: 

Friday, July 18, 2014 - 1:00pm

Seminar Location: 

  • JILA X317

Speaker Name(s): 

Leonid Isaev

Speaker Affiliation(s): 

Louisiana State University, Department of Physics & Astronomy
Seminar Type/Subject

Scientific Seminar Type: 

  • JILA Public Seminar

Event Details & Abstract: 

The Kondo effect describes screening of a single local spin by mobile electrons. A natural realization of the Kondo physics is provided by so-called heavy-fermion materials, such as CeCoIn5, where localized electron states originating from atomic f-shells (of Ce ions) interact with the conduction band. However, majority of such compounds actually feature degenerate
$f$-levels which in addition to the spin quantum number possess an orbital degree of freedom. The latter not only participates in the Kondo effect, but may also order at sufficiently low temperature. This orbital ordering is generally believed to compete with the Kondo screening.
 
In my talk, I will discuss an opposite scenario and present a mechanism for the Kondo effect-assisted orbital order in f-electron systems. The key ingredient of our analysis is the Hund interaction between local electrons which is dynamically frustrated by the formation of the Kondo resonance. I will illustrate this mechanism by considering the periodic two-orbital Anderson model with two local electrons, and show how the Hund's rule frustration gives rise to an incommensurate spiral magneto-orbital order inside the Kondo screened (heavy-electron) phase. This state may be observed in neutron and X-ray measurements on U- and Pr-based heavy-fermion compounds.